Oxygen atom transfer mediated by an iron(IV)/iron(II) macrocyclic complex containing pyridine and tertiary amine donors

A new non-heme iron model complex containing a high-spin iron(II) complexed with N-methylated pyridine-containing macrocycle was synthesized and crystallographically characterized. The complex generates peroxo- and high-valent iron-oxo intermediates in reactions with tert-butylhydroperoxide and isopropyl 2-iodoxybenzoate, respectively, allowing to gain insight into the formation and reactivity of enzyme-like intermediates related to biological oxygen activation. The formation and reactivity of these intermediate species were investigated by the stopped-flow methodology. The mechanism of oxygen transfer to organic substrates involving reaction of oxoiron(IV) intermediate was elucidated on the basis of spectroscopic and kinetic data. Incorporation of a pyridine ring into the macrocycle increased the reactivity of the FeIVO intermediates in comparison with polyamine tetraaza macrocyclic complexes: ferryl (FeIVO) species derived from 3 demonstrated electrophilic reactivity in transferring an oxygen atom to substituted triarylphosphines and to olefins (such as cyclooctene). However, iron(III) alkylperoxo intermediate was unreactive with cyclooctene.

Ferryl (FeIVO) species derived from 3 demonstrated electrophilic reactivity in transferring an oxygen atom to substituted triarylphosphines and to olefins (such as cyclooctene); however, iron(III) alkylperoxo intermediate was unreactive with cycloocteneFigure optionsDownload as PowerPoint slideHighlights
► N-methylated pyridine azamacrocycle (PyMAC) folds upon binding iron(II), forming a high-spin complex.
► Reaction with t-Buhydroperoxide yields an alkylperoxo intermediate that does not oxidize substrates.
► Reaction with iodine(V) yields an electrophilic Fe(IV)O intermediate that epoxidizes olefins.
► Kinetic parameters for these reactions were determined by the low temperature stopped-flow method.